Rockers too high on the studs?

[GARY C]

Have you checked to see what length push rod gives you the best lift?

[MadBill]

I’m measuring for pushrod length and something seems off here. It doesn’t seem to matter what length I set my adjustable pushrod measuring tool at...each time the tip pattern is nice and tight even if it isn’t in the center...

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Looks like you're closing in on a resolution, but a couple of comments:
First, by pure geometry, the sweep cannot remain the same when the pushrod length (and thus the rocker angle) changes, as a simple drawing will show.
Also, unless your gross lift is less than 0.400", the photo shows a too long pushrod, since the rocker-to-retainer "up" angle above the retainer with a closed valve will clearly be much smaller than the "down" angle at full lift, as the Straub/"90° at half lift" approach ensures.
Lastly, not all will agree, but the pushrod length should not be changed to center the roller. If it isn't in danger of overhanging the valve tip leave it be, to maintain minimum sweep. If it's far out, you need a different rocker.

[Geoff2]

Looks like the rocker is too small. That will sit the rocker higher on the stud & might cause the p'rod to contact the rocker at max lift.

[PRH]

Lastly, not all will agree, but the pushrod length should not be changed to center the roller. If it isn't in danger of overhanging the valve tip leave it be, to maintain minimum sweep. If it's far out, you need a different rocker.

Exactly.

If it’s too far out...... or too far in..... when the geometry is correct..... the length of the rocker is wrong for the head.

[gmrocket]

I’m measuring for pushrod length and something seems off here. It doesn’t seem to matter what length I set my adjustable pushrod measuring tool at...each time the tip pattern is nice and tight even if it isn’t in the center. I ended up getting a nice tight sweep pattern in the center of the tip with my comp 7703 tester set at 8.000”, which seems too long for this combo. I’m using light test springs and am just taking out the lash, being careful not to compress the lifter plunger or move the valve while the cam is on the base circle. Set at 8.000”, it seems that the rockers end up too high on the stud. What am I doing wrong here?

351w decked to 9.480”, Promaxx 9175 heads, Jones small hydraulic roller, PBM 1.6 rockers, Howard’s good link bar lifters (not the cheap ones).


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If you say the sweep is good no matter what length you use, start at the normal length p Rod dimension, measure from outside edge of retainer to outer edge of roller wheel at zero lash , then again at max lift.

See what the ratio actually is

Then do the same again at something like +.050 and see what you get.

I would also check lift at a few points and max.

[Paul Kane]

First of all, how is the rocker positioned in the picture?

• Is the rocker arm at rest with the lifter on the base circle of the cam and the valve closed?
• Or is the rocker arm at mid-lift?
• Or is it at full open?

Please specify.

[n2omike]

The rocker should be fairly square/perpendicular with the stud at mid-lift. Sometimes, you can get way out of whack going for the narrowest sweep. Get the sweep about as narrow as you can... while keeping the rocker fairly square to the stud at mid lift.

This being said, Chevy rockers are shorter than ford rockers from the pivot to the tip. Ford rockers should be used on Ford heads, but on some early Twisted Wedge heads, Chevy rockers work better. Also make sure you are using a name brand rocker... not Chinese crap. Scorpion makes a nice, affordably priced rocker.

Sweep should be no more than 0.080" and be fairly centered on the valve.

Good Luck

[PRH]

First of all, how is the rocker positioned in the picture?

• Is the rocker arm at rest with the lifter on the base circle of the cam and the valve closed?
• Or is the rocker arm at mid-lift?
• Or is it at full open?

Please specify.

Based on how both valves are at the same tip height...... sure looks like fully closed to me.

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[SchmidtMotorWorks]

The pivot level should be about 1/2 of lift below the valve tip, measured along the axis of the valve.

So, your pushrod is way too long.

Hopefully that will bring the socket to an acceptable position but it looks like the socket is positioned too high in the rocker.
I suspect that you will need a different rocker.

rocker.jpeg

[midnightbluS10]

Two things I really try and stay away from are Chinese rockers and dampers.

According to PBM, their rockers are made in the USA.

[travis]

In the photo, the valves are closed.

I tried the Straub method, and got a measurement of 7.875". Still a nice tight sweep pattern as before, just closer to the intake...an still appears to be sitting wrong. 7.700" (which should be pretty close) is closer to the intake yet, and still too high.

I've got a set of Scorpion rockers on order now...

[Geoff2]

If you check it out on the net, you should find pics of Scorpion rockers with cracks in the body where the roller tip shaft is; also, pics of the anodising flaking off around the trunnion area....which means the alum is stretching & not happy. There is a reason quality rockers like Crowers cost more....

[travis]

If you check it out on the net, you should find pics of Scorpion rockers with cracks in the body where the roller tip shaft is; also, pics of the anodising flaking off around the trunnion area....which means the alum is stretching & not happy. There is a reason quality rockers like Crowers cost more....

You’re killing me Smalls!

So considering the application, what would you (any of you) consider to be a good quality rocker for this?

[turbo camino]

I used to have a Big Chief-headed motor that would pretty regularly eat several needle bearings in the Jesel rockers. Nothing is indestructible no matter what it costs.

[GerryP]

I used to have a Big Chief-headed motor that would pretty regularly eat several needle bearings in the Jesel rockers. Nothing is indestructible no matter what it costs.

Except anvils.